Add GitHub Copilot review instructions

[JasonSooter]

Before this PR

• Relied upon the default. Not specific enough

After this PR

• Introduce comprehensive review instructions for GitHub Copilot to enhance code quality and maintainability in the Twilio Segment Destination Function template. The document outlines project context, review philosophy, repository-specific patterns, a checklist for code review, common pitfalls, and a structured review response format. This aims to ensure high standards in code reviews and facilitate continuous improvement.

Reason that prompted this change

• Inspired by this post
• GitHub Copilot PR Review is an available feature that can help with code quality

Test Plan

• No impact

[Copilot]

Pull request overview

This PR introduces comprehensive GitHub Copilot review instructions for a Twilio Segment Destination Function template. The document provides detailed guidelines, code examples, and best practices to standardize code reviews for JavaScript-based Segment functions.

Key changes:

• Establishes review philosophy emphasizing production stability and maintainability
• Documents repository-specific patterns including conditional exports and async function requirements
• Provides a comprehensive checklist covering functional requirements, error handling, performance, testing, security, code style, and deployment considerations

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💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.